* In cumulus/plugins.block.Block.{place,doPnr}(), reorder the
feed insertion and spare buffer deletion call. Formerly, we
were :
1. Creating spare buffersa (Python).
2. Placing (C++)
3. Adding feeds (EtesianEngine::toHurricane() call) (C++).
4. Removing unused spare buffers (Python).
So, step 4 was *not* informing the C++ placement data-structure
created at step 3 of the change. Resulting in occurrences using
deleted Entities (Instance).
Now we swap step 3. and 4. so toHurricane() is called *after*
any Python managed change is done.
Ideally, what we should implement is a way for Python to inform
the C++ data-structure. No real problem here, but time...
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